Surface coupled laser and laser optical interposer

ABSTRACT

An example system includes a grating coupled laser, a laser optical interposer (LOI), an optical isolator, and a light redirector. The grating coupled laser includes a laser cavity and a transmit grating optically coupled to the laser cavity. The transmit grating is configured to diffract light emitted by the laser cavity out of the grating coupled laser. The LOI includes an LOI waveguide with an input end and an output end. The optical isolator is positioned between the surface coupled edge emitting laser and the LOI. The light redirector is positioned to redirect the light, after the light passes through the optical isolator, into the LOI waveguide of the LOI.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.16/438,414, filed Jun. 11, 2019, which is a Divisional of U.S. patentapplication Ser. No. 15/834,040, filed Dec. 6, 2017, which claims thebenefit of and priority to U.S. Provisional App. No. 62/430,797, filedDec. 6, 2016. The foregoing applications are incorporated herein byreference.

FIELD

The embodiments discussed herein are related to surface coupled systemsthat include a surface coupled laser and a laser optical interposer(LOI).

BACKGROUND

Unless otherwise indicated herein, the materials described herein arenot prior art to the claims in the present application and are notadmitted to be prior art by inclusion in this section.

Coupling light from single mode edge emitting lasers to silicon (Si)photonics is costly, as it generally requires two lenses and a largeisolator block. In systems that include such lasers and Si photonics,alignment tolerances may be less than 0.5 micrometers (μm). Such lowalignment tolerances typically require active alignment to be met.

The subject matter claimed herein is not limited to implementations thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some implementationsdescribed herein may be practiced.

BRIEF SUMMARY OF SOME EXAMPLE EMBODIMENTS

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential characteristics of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

Some embodiments described herein generally relate to surface coupledsystems that include a surface coupled laser and a LOI.

In an example embodiment, a system includes a grating coupled laser, aLOI, an optical isolator, and a light redirector. The grating coupledlaser includes a laser cavity and a transmit grating optically coupledto the laser cavity. The transmit grating is configured to diffractlight emitted by the laser cavity out of the grating coupled laser. TheLOI includes an LOI waveguide with an input end and an output end. Theoptical isolator is positioned between the surface coupled edge emittinglaser and the LOI. The light redirector is positioned to redirect thelight, after the light passes through the optical isolator, into the LOIwaveguide of the LOI.

In another example embodiment, a method includes emitting light from anactive section of a grating coupled laser. The method also includesdiffracting the light out of the grating coupled laser at a transmitgrating of the grating coupled laser. The method also includes passingthe light through an optical isolator positioned in an optical path ofthe light. The method also includes redirecting the light to propagatein a horizontal direction into a LOI waveguide of a LOI. The method alsoincludes receiving the light propagating horizontally into the LOIwaveguide.

In an example embodiment, a system includes a grating coupled laser, aLOI, and a light redirector. The grating coupled laser includes a lasercavity and a transmit grating optically coupled to the laser cavity. Thetransmit grating is configured to diffract light emitted by the lasercavity out of the grating coupled laser. The LOI includes an LOIwaveguide with an input end and an output end. The light redirector isoptically positioned between the grating coupled laser and the LOI. Thelight redirector is configured to redirect the light received from thegrating coupled laser and traveling in a first direction to travel in asecond direction into the input end of the LOI waveguide, the seconddirection parallel to the LOI waveguide.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 illustrates an example surface coupled system;

FIGS. 2A and 2B illustrate an example surface coupled edge emittinglaser that may be implemented in a surface coupled system;

FIG. 2C illustrates another example surface coupled edge emitting laserthat may be implemented in a surface coupled system;

FIG. 3 illustrates another example surface coupled system that includesa LOI;

FIG. 4 illustrates derivation of an interface angle θ of an inputinterface of the LOI of FIG. 3;

FIG. 5 illustrates an overhead view and cross-sectional views of anexample LOI;

FIG. 6 illustrates cross-sectional views of an example LOI with twovertically separated and parallel waveguide cores;

FIG. 7 illustrates another example surface coupled system;

FIG. 8 illustrates an overhead view and cross-sectional views of anotherexample LOI;

FIG. 9 is a cross-sectional view of another example LOI;

FIG. 10 illustrates a simulated input optical mode of the LOI of FIG. 9;

FIG. 11A includes a cross-sectional view of another example LOI;

FIG. 11B includes an overhead view of first and second waveguide coresof the LOI of FIG. 11A;

FIG. 12 illustrates a portion of the LOI of FIG. 11A;

FIG. 13 is a simulation of conversion efficiency as a function of lengthof a SSC section of the LOI of FIG. 11A;

FIG. 14 illustrates the LOI and a Si PIC of FIG. 11A;

FIG. 15 illustrates an example surface coupled system with a firstlaser-to-LOI coupling configuration;

FIG. 16 illustrates another example surface coupled system with a secondlaser-to-LOI coupling configuration;

FIG. 17 illustrates another example surface coupled system with a thirdlaser-to-LOI coupling configuration;

FIG. 18 illustrates another example surface coupled system with a fourthlaser-to-LOI coupling configuration;

FIG. 19 illustrates another example surface coupled system with a fifthlaser-to-LOI coupling configuration; and

FIG. 20 illustrates another example surface coupled system with a sixthlaser-to-LOI coupling configuration,

all arranged in accordance with at least one embodiment describedherein.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

U.S. Publication No. 2017/0179680, published Jun. 22, 2017 (hereinafterthe '680 publication), and U.S. Pat. No. 9,405,066, issued Aug. 2, 2016(hereinafter the '066 patent) are incorporated herein by reference.

Some embodiments described herein and/or in the '680 publication removethe need for lenses in systems such as those described in theBACKGROUND, which may reduce part count and cost, and significantlysimplify packaging processes in such systems. An isolator may be used insuch systems. The absence of lenses in such systems may significantlyreduce the size and cost of the isolator and may significantly increasealignment tolerances. For example, the alignment tolerance may beincreased by a factor of 10 or even 50 or more from about 0.1 μm whichhas to be done by active feed-back alignment, which requires turning onthe laser during alignment, to about 1-2 μm or even 5-8 μm or moreachieved in a passive alignment pick- and place machine; i.e. withouthaving to turn on the laser. Alternatively or additionally, embodimentsdescribed herein may enable wafer level testing of lasers.

According to some embodiments disclosed in the '680 publication, asurface coupled system including a first surface grating (or firstdiffraction grating or transmit grating) and a second surface grating(or second diffraction grating or receive grating) is provided to couplelight from an edge emitting laser to a PIC, such as a Si PIC. In someembodiments, the first and second surface gratings may each include asmall index contrast long surface grating. In general, a small indexcontrast long surface grating may include a surface grating with anindex contrast less than about 1-1.5 and a length greater than 10 μm. Inother embodiments, the first and second surface gratings may eachinclude a large area surface grating (LASG) with a length greater thanabout 10 μm and with or without small index contrast.

The edge emitting laser may include an indium phosphide (InP) laser orother suitable edge emitting laser. The InP laser may include an inputpassive waveguide that expands in a fan out region to the first surfacegrating. The first surface grating may be configured to generate arelatively large optical mode spot size of about 8-40 μm for an opticalbeam diffracted by the first surface grating. Such an edge emittinglaser formed in the same chip with a transmit grating may be referred toherein as a surface coupled edge emitting laser.

According to embodiments described in the '680 publication, the receivegrating may be formed in the Si PIC. The receive grating may beconfigured to receive the light diffracted by the transmit grating andto redirect the light into a waveguide of the Si PIC.

Embodiments described in the '680 publication additionally includeaspects of the first diffraction grating. In an example embodiment, asurface coupled system may include a surface coupled edge emitting laserand a PIC. The surface coupled edge emitting laser may include a firstwaveguide and a first diffraction grating optically coupled to the firstwaveguide. The PIC may include a second waveguide and a seconddiffraction grating optically coupled to the second waveguide. The firstwaveguide of the surface coupled edge emitting laser may include a corewith a core index of refraction, a top cladding with a top claddingindex of refraction, and a substrate as a bottom cladding with a bottomcladding index of refraction. The first diffraction grating may includegrating teeth formed on the core of the first waveguide, the gratingteeth may each have a total height, a height above the core of the firstwaveguide, a period, and a duty cycle. The core index of refraction maybe greater than a first threshold value so that an effective index ofthe first diffraction grating is sufficiently higher than the bottomcladding index to avoid leakage of a diffracted optical mode into thesubstrate.

The first surface grating mentioned above may alternatively oradditionally be referred to as a first diffraction grating or a transmitgrating. The second surface grating mentioned above may alternatively oradditionally be referred to as a second diffraction grating or a receivegrating. As used herein, “transmit grating” may generally refer to adiffraction grating included in a passive section of a surface couplededge emitting laser which diffracts light from a laser cavity of thesurface coupled edge emitting laser downward through a substrate and/orother layers towards the Si PIC. As used herein, “receive grating” maygenerally refer to a diffraction grating included in the Si PIC whichreceives the light from the transmit grating and directs it into awaveguide in the Si PIC.

Receive gratings in Si PICs may have coupling loss that is higher thandesired for at least some applications. Alternatively or additionally,receive gratings may have insufficient bandwidth for some applicationslike coherent optics. Embodiments described herein include variousalternatives to receive gratings.

In an example embodiment, a system includes a surface coupled edgeemitting laser, a LOI, and an optical isolator. The surface coupled edgeemitting laser includes a first waveguide and a transmit gratingoptically coupled to the first waveguide. The LOI includes a LOIwaveguide and an input interface. The optical isolator is positionedbetween the surface coupled edge emitting laser and the LOI. The LOI ispositioned to receive light output by the surface coupled edge emittinglaser that is diffracted downward through the optical isolator by thetransmit grating. The input interface of the laser optical interposer isconfigured to redirect the output beam into the LOI waveguide.

The system may additionally include a single mode fiber (SMF)butt-coupled to the LOI waveguide. In these and other embodiments, anoptical mode of an input end of the LOI waveguide may match orsubstantially match an optical mode of the light output by the surfacecoupled edge emitting laser. Alternatively or additionally, an opticalmode of an output end of the LOI waveguide may match or substantiallymatch an optical mode of the SMF. Thus, the LOI may change the opticalmode of the light from the input end to the output end. For instance, inan example embodiment, the input end of the LOI has a w₀ parameter in arange from 10 micrometers (μm) to 15 μm and the output end of the LOIhas a w₀ parameter in a range from 4 μm to 5 μm. Two optical modes maybe said to match if their profiles overlap by at least 70%, at 80%, atleast 90%, or some other threshold.

In some embodiments, the system may include a PIC with a waveguide witha tapered end. The waveguide may include a silicon nitride (SiN)waveguide. The tapered end of the waveguide, and specifically of awaveguide core of the waveguide, in the PIC may be positioned beneaththe output end of the LOI waveguide. The tapered end may be aligned intwo orthogonal directions with the output end of the LOI waveguide. TheLOI waveguide and the tapered end of the waveguide in the PIC may forman adiabatic coupler, e.g., as described in the '066 patent.

Reference will now be made to the drawings to describe various aspectsof example embodiments of the invention. It is to be understood that thedrawings are diagrammatic and schematic representations of such exampleembodiments, and are not limiting of the present invention, nor are theynecessarily drawn to scale.

FIG. 1 illustrates an example surface coupled system 100 as described inthe '680 publication. As illustrated, the surface coupled system 100 mayinclude a surface coupled edge emitting laser (hereinafter “laser”) 102and a Si PIC 104. Surface coupled edge emitting lasers such asillustrated in FIG. 1 and other Figures herein may alternatively oradditionally be referred to as grating coupled lasers (GCLs) or GCLlasers. In the example of FIG. 1, the laser 102 includes an InP laser.The surface coupled system 100 of FIG. 1 may additionally include anoptical isolator 120 disposed between the laser 102 and the Si PIC 104.

The laser 102 may include a first surface grating 106 and the Si PIC 104may include a second surface grating 108. The first surface grating 106may be optically coupled to an active section 112 of the laser 102through a core waveguide. The core waveguide may be optically coupled toreceive light emitted by a gain medium (not illustrated) of the activesection 112 of the laser 102. In some embodiments, a fan out region maybe provided between the core waveguide and the first surface grating 106and/or may include the core waveguide. The fan out region may be formedfrom a same medium and layer as the core waveguide such that the fan outregion may generally be an extension of the core waveguide.Additionally, the fan out region may include grating lines such that thefan out region may generally be an extension of the first surfacegrating 106.

The light emitted from the active section 112 of the laser 102 maytravel through the core waveguide to the fan out region, where a mode ofthe light may be expanded laterally (e.g., generally in and out of thepage in FIG. 1). The first surface grating 106 may diffract the lightwith the laterally expanded mode generally downward as diffracted light110. The diffracted light 110 may be diffracted toward the secondsurface grating 108 of the Si PIC 104. The mode of the diffracted light110 may be expanded to a 8-40 μm spot size (lateral measurement) withinthe fan out region while simultaneously being expanded along thedirection of the active section 112 by the first surface grating 106.One potential benefit of this method of expanding diffracted light maybe that the spot size may be much larger than the 2 to 4 μm spot sizethat can be achieved with standard spot size converters.

The diffracted light 110 may be received by the second surface grating108. The diffracted light 110 may be redirected by the second surfacegrating 108 into a waveguide (not illustrated) of the Si PIC 104. Oneexample of the waveguide may be a Si waveguide.

The diffracted light 110 passes through the optical isolator 120 beforereaching the second surface grating 108 of the Si PIC 104. The opticalisolator 120 may be configured to reduce or eliminate back reflection.The optical isolator 120 may be attached to the Si PIC 104, or to thelaser 102, or to both the Si PIC 104 and the laser 102.

FIGS. 2A and 2B illustrate an example surface coupled edge emittinglaser (hereinafter “laser”) 202A that may be implemented in a surfacecoupled system, such as the surface coupled system 100 discussed inrelation to FIG. 1 and in the surface coupled system 300 of FIG. 3 andin other surface coupled systems described herein. FIG. 2A includes abottom view and FIG. 2B includes a bottom perspective view of the laser202A. FIG. 2C illustrates another example surface coupled edge emittinglaser (hereinafter “laser”) 202B that may be implemented in a surfacecoupled system, such as the surface coupled system 100 discussed inrelation to FIG. 1, the surface coupled system 300 of FIG. 3, or othersurface coupled systems described herein. Each of the lasers 202A and202B may include or correspond to the laser 102 of FIG. 1 or to otherlasers in other systems described herein.

Referring first to FIGS. 2A and 2B, the laser 202A may include a gainmedium 216, a first distributed Bragg reflector (DBR) 214A, and a secondDBR 214B. The first and second DBRs 214A-B together with the gain medium216 may form a laser cavity 212 such that the laser 202A in the exampleof FIGS. 2A and 2B may include a DBR laser. Alternatively oradditionally, and as illustrated in FIG. 2C, the laser 202B may includea distributed feedback (DFB) laser in which a grating 220 and gainmedium 222 overlap in the laser cavity. In other embodiments, a DFB typegain region and one or more passive DBR regions may both be present toprovide feedback in a configuration which may be termed a DistributedReflector (DR) laser, and which may be used for high speed laserapplications. Each of the lasers 202A, 202B may include a first surfacegrating 206 optically coupled to the corresponding laser cavity (e.g.,212 in FIGS. 2A and 2B). The first surface grating 206 may be similar oridentical to the first surface grating 106 discussed in relation to FIG.1 or to other first surface gratings discussed herein. A fan out regionof the first surface grating 206 may include grating lines such that thefirst surface grating 206 and the fan out region partially or completelyoverlap.

In FIGS. 2A and 2B, a reflectance of the second DBR 214B may be about 98percent and a reflectance of the first DBR 214A may be about 30 percent.In other embodiments, the first and second DBRs 214A-B may have otherreflectance values.

The laser 202A may generally emit light 218 through the first DBR 214Atoward the first surface grating 206. The emitted light 218 may interactwith the first surface grating 206 to be diffracted by the first surfacegrating 206 as diffracted light 210.

In FIG. 2C, the laser 202B implemented as a DFB laser may generally emitlight 224 through a front of the DFB laser toward the first surfacegrating 206. The light 224 may interact with the first surface grating206 to be diffracted by the first surface grating 206 as diffractedlight 226.

The laser 202A and/or 202B may be hermetically sealed by a passivationlayer formed by SiN or silicon oxide (SiO_(x)) deposition on the laser202A or 202B. In more detail, one or more layers of SiN and/or SiO_(x)may be deposited over the laser 202A or 202B to hermetically seal thelaser 202A or 202B.

The surface coupled system 100 of FIG. 1 is an example of a relativelysimple integration scheme for coupling light from the laser 102 to theSi PIC 104. However, some implementations of the configuration of FIG. 1may be subject to undesirably high coupling loss, limited bandwidth,and/or back reflection. Embodiments described herein relate to analternative coupling scheme to couple light from a GCL laser to a Si PICthat may have lower loss, wider bandwidth, and/or less back reflectionthan the configuration of FIG. 1.

Accordingly, FIG. 3 illustrates another example surface coupled system300, arranged in accordance with at least one embodiment describedherein. As illustrated, the surface coupled system 300 may include a GCLlaser 302, a LOI 310, an optical isolator 320, and a Si PIC The GCLlaser 302 and the optical isolator 320 may be the same or similar to theother lasers and optical isolators described herein and/or in the '680publication. For instance, the GCL laser 302 may include an activesection/laser cavity 312 and first surface grating 306 similar to thelaser 102 of FIG. 1 and may function in the same or similar way, whilethe optical isolator 320 may function in the same or similar way as theoptical isolator 120.

The LOI 310 includes an LOI waveguide 314 and an input interface 316(labeled “Reflecting interface” in FIG. 3). The LOI 310 may additionallyinclude an exit facet 318. The LOI waveguide 314 may include a waveguidecore 322 and a cladding 324. The waveguide core 322 may include SiN andthe cladding 324 may include silicon dioxide (SiO₂) in some embodiments.In other embodiments, the LOI 310 may include a high index glasswaveguide formed by ion exchange process.

In operation, light 326 is output generally downward from the GCL laser302, and more particularly at an angle ϕ relative to a normal line fromthe GCL laser 302, which normal line may be vertical assuming the GCLlaser 302 is positioned with the first surface grating 306 parallel tohorizontal. The light 326 passes through the optical interposer 320 anda top of the LOI 310 and interacts with the input interface 316 of theLOI 310. Assuming the LOI 310 is positioned with its upper and lowersurfaces parallel to horizontal, the input interface 316 may be angledrelative to vertical at an interface angle θ selected to redirect thelight into the LOI waveguide 314 traveling horizontal. The inputinterface 316 may redirect the light by reflection, e.g., total internalreflection.

The waveguide core 322 of the LOI waveguide 314 may have a higher indexof refraction than the cladding 324 of the LOI waveguide 314. The LOI310 may be surrounded by air or other surrounding material of lowerindex of refraction than the cladding 324 of the LOI waveguide 314 tocause the light 326 from the GCL laser 302 that reaches the inputinterface 316 to reflect in the horizontal direction into the waveguidecore 322 of the LOI waveguide 314.

The Si PIC 304 includes a waveguide 328 with a tapered end 330. Thewaveguide 328 of the Si PIC 304 may include a SiN waveguide, e.g., a SiNwaveguide core surrounded by cladding. Discussion of tapering or atapered end of this and other waveguides may more particularly refer totapering or a tapered end of the waveguide core unless context indicatesotherwise.

The tapered end 330 of the waveguide 328 in the Si PIC may be positionedbeneath an output end of the LOI waveguide 314. The tapered end 330 maybe aligned in two orthogonal directions with the output end of the LOIwaveguide 314. The LOI waveguide 314 and the tapered end 330 of thewaveguide 328 in the Si PIC 304 may form an adiabatic coupler, e.g., asdescribed in the '066 patent. In these and other embodiments, taperwidth and shape of the tapered end 330 of the waveguide 328 in the SiPIC 304 may be designed such that at some point along the length of thetapered end 330, effective index of the optical mode in the LOIwaveguide 314 substantially matches effective index of the tapered end330 of the waveguide 328. As such, the light traveling in the LOIwaveguide 314 may be adiabatically coupled from the LOI waveguide 314into the waveguide 328 in the Si PIC 304.

Equations (1)-(4) together with FIG. 4 illustrate derivation of theinterface angle θ of the input interface 316 of the LOI 310 of FIG. 3,arranged in accordance with at least one embodiment described herein.

$\begin{matrix}{{\sin (\gamma)} = {n_{InP}{\sin (\phi)}}} & (1) \\{{\sin (\alpha)} = {{\sin (\gamma)}/n_{G}}} & (2) \\{\theta = {\left( {90 - \alpha} \right)/2}} & (3) \\{\theta = {45 - {\frac{1}{2}{\sin^{- 1}\left( \frac{n_{InP}{\sin (\phi)}}{n_{G}} \right)}}}} & (4)\end{matrix}$

In FIG. 4 and equations (1)-(4), and assuming the first surface grating306, the optical isolator 320, and the LOI 310 are all oriented parallelto horizontal, φ is the diffraction angle of the light 326 from thefirst surface grating 306, γ is both the angle of incidence of the light326 at the optical isolator 320 and the angle of departure of the light326 from the optical isolator 320, α is the propagation angle of thelight 326 through the LOI 310 relative to vertical, θ is the interfaceangle of the input interface 316, n_(InP) is the index of refraction ofa substrate of the GCL laser through which the light 326 passes, andn_(G) is the index of refraction of the LOI 310, or at least of thecladding of the LOI 310.

In an example embodiment, and as illustrated in FIG. 4, the opticalisolator 320 may include a first polarizer 320A, a Garnet or otherFaraday Rotator 320B, and a second polarizer 320C.

From Snell's law, the interface angle θ of the input interface 316 ofthe LOI 310 is given from equations (1)-(3) by equation (4). As anexample, if the index of refraction n_(InP) is 3.25 and the index ofrefraction n_(G) of the LOI 310 is 1.467, then the diffraction angle φfrom the transmit grating may be about 14 degrees and the interfaceangle θ of the input interface 316 of the LOI 310 may be about 28.5degrees. In some embodiments, the indices of refraction of the firstpolarizer 320A, the Garnet 320B, and the second polarizer 320C that makeup the optical isolator 320 may be irrelevant to the derivation of theinterface angle θ as long as the surfaces of each are parallel to eachother. In this and other embodiments, the angle γ at the input and theoutput of the optical isolator 320 may remain the same, only theposition at which the light 326 enters and exits the optical isolator320 may change. More generally, however, the angle(s) at which lightenters and exits the optical isolator 320 may be considered if surfacesof the optical isolator 320 are not parallel to each other.

FIG. 5 illustrates an overhead view and cross-sectional views of anexample LOI 500, arranged in accordance with at least one embodimentdescribed herein. The LOI 500 may include or correspond to the LOI 310of FIGS. 3 and 4 or to other LOIs in other surface coupled systemsdescribed herein. FIG. 5 and other Figures herein include anarbitrarily-defined x-y-z reference frame. In the x-y-z reference frame,the x axis is oriented vertically, the y axis is oriented laterally, andthe z axis is oriented in a light propagation direction.

In the example of FIG. 5, the LOI 500 includes a waveguide core 502 andsurrounding cladding 504 that together form an LOI waveguide of the LOI500. As illustrated in the overhead view of FIG. 5 (top diagram), thewaveguide core 502 includes an input end 506 that is tapered, and anoutput end 508 that may or may not be tapered. The input end 506 and/orthe output end 508, to the extent tapered, may be tapered in a singledimension, e.g., laterally (y direction) or vertically (x direction), orin two dimensions, e.g., laterally and vertically. In the example ofFIG. 5, the input end 506 is tapered in the lateral direction and isnarrowest at a leftmost point of the input end 506, the input end 506widening from left to right in FIG. 5. The two cross-sectional views ofFIG. 5 depict example widths of the waveguide core 502 at the leftmostpoint of the waveguide core 502 in the cross-sectional view on the leftand at the rightmost point of the waveguide core 502 in thecross-sectional view on the right.

Each of the cross-sectional views of FIG. 5 additionally illustrates acorresponding example optical mode 510, 512 of the LOI 500 at the inputend 506 and the output end 508. Each of the optical modes 510, 512 isgenerally Gaussian and may be characterized by a parameter w₀. Theparameter w₀ may refer to half the width of the Gaussian optical modeintensity at 1/e² of its peak height. In general, the optical mode maybe less confined with smaller waveguide core. Thus, the optical mode maybe less confined at the input end 506 and more confined at the outputend 508 of the waveguide core 502 of the LOI waveguide. As an example,the w₀ parameter of the optical mode 510 at the input end 506 may be ina range from 10-15 μm, while the w₀ parameter of the optical mode 512 atthe output end 508 may be in a range from 4-5 μm. More generally, theLOI waveguide may be configured so that the input end 506 has an opticalmode 510 that substantially matches an optical mode of the light outputfrom a corresponding GCL laser and so that the output end 508 has anoptical mode 512 that substantially matches an optical mode of awaveguide of a Si PIC (e.g., the waveguide 328 of the Si PIC 304 of FIG.3) or of a SMF.

In the cross-sectional views of FIG. 5, the LOI waveguide includes asingle waveguide core 502. In other embodiments, the LOI waveguide mayinclude two or more waveguide cores, which together form an effectivesingle mode waveguide. Examples of such LOI waveguides have beendisclosed by LIONIX BV. The two or more waveguide cores may include thesame or different footprints. For example, FIG. 6 illustratescross-sectional views of an example LOI 600 with two verticallyseparated and parallel waveguide cores 602A, 602B (hereinaftercollectively “waveguide cores 602”), arranged in accordance with atleast one embodiment described herein. The left-most cross-sectionalview of the LOI 600 may be of an input end of the LOI 600 while theright-most cross-sectional view of the LOI 600 may be of an output endof the LOI 600. In the example of FIG. 6, the two waveguide cores 602have the same footprint as each other and may have the same or similarfootprint as the waveguide core 502 as illustrated in the overhead viewof FIG. 5. For example, each of the two waveguide cores 602 in FIG. 6may be relatively narrower at the input end as illustrated in theleftmost cross-sectional view of FIG. 6 tapering output to be relativelywider at the output end as illustrated in the rightmost cross-sectionalview of FIG. 6.

Each of the cross-sectional views of FIG. 6 additionally illustrates acorresponding example optical mode 610, 612 of the LOI 600 at,respectively, the input end and at the output end of the LOI 600. As inFIG. 5, the optical mode 610 may be less confined at the input endwhereas the optical mode 612 may be more confined at the output end ofthe waveguide cores 602 of the LOI 600.

A variety of configurations can be used to achieve the desired waveguideproperties for the LOI waveguide of one or more of the LOIs describedherein. In an example, the LOI waveguide includes one or more SiNwaveguide cores with silicon dioxide (SiO₂) cladding. Each of the one ormore SiN waveguide cores may have thin rectangular cross-sectionalprofiles as illustrated in FIGS. 5 and 6, with thicknesses (e.g., in thevertical direction) of 200-300 nanometers (nm) and varying widths forthe taper and that are single mode for TE polarization. By tapering thewidth (e.g., the y dimension) of the one or more waveguide cores, theoptical mode may be modified to match w₀=10-15 μm on the entrance of theLOI waveguide to match the mode out of a transmit grating of a GCLlaser, and optionally to match a SMF at the exit facet of the LOI. Thesame or similar configuration can be used to adiabatically couple lightfrom the LOI waveguide to a SiN waveguide with a tapered end in a SiPIC, e.g., as illustrated in FIG. 3.

FIG. 7 illustrates another example surface coupled system 700, arrangedin accordance with at least one embodiment described herein. The surfacecoupled system 700 of FIG. 7 includes the GCL laser 302 and the opticalisolator 320 of FIG. 3. The surface coupled system of FIG. 7additionally includes an LOI 710 and a SMF 704 instead of the Si PIC 304of FIG. 3. The LOI 710 may be the same as or similar to the LOIs 310,500, 600 of FIGS. 3-6 provided an optical mode at the output of the LOI710 is configured to match an optical mode of the SMF 704.

FIG. 7 additionally includes example optical modes 712, 714, 716, 718 ofthe light 326 generated by the GCL laser 302 at various points in thesurface coupled system 700 of FIG. 7. As illustrated in FIG. 7, theoptical mode 714 at an input end (e.g., left side) of the LOI 710substantially matches the optical mode 712 output from the first surfacegrating 306, while the optical mode 716 at an output end (e.g., theright side) of the LOI 710 substantially matches the optical mode 718 ofthe SMF 704.

In the example of FIG. 7, the output of the LOI 710 may be directlybutt-coupled to the SMF 704. The GCL laser 302 may be a high speeddirectly modulated laser (DML), in which case the Si PIC (e.g., the SiPIC 304 of FIG. 3) may be omitted and the light 326 in the form of anoptical signal may be directly generated in the GCL laser 302 and outputto the SMF 704 through the optical isolator 320 and the LOI 710. Withreference to FIG. 3, where the GCL laser 302 is not a DML, however, thelight 326 may be generated by the GCL laser 302 as an optical beam thatis output through the optical isolator 320 and the LOI 310 into the SiPIC 304, which may include an external modulator to convert the opticalbeam to an optical signal.

Returning to FIG. 7, the first surface grating 306 in the GCL laser 302,which may include an InP laser, may function as a very large spot sizeconverter, generating a spot size of 10-20 μm full width at half maximum(or a divergence angle of 1 degree) not achievable by standard taperingin InP. Typical divergence angle for conventional DMLs may be roughly10-20 times higher than the example embodiment of FIG. 7. The large spotand small divergence according to embodiments described herein allow theoptical isolator 320 to be packaged without critical alignment due to analignment accuracy of 5-8 μm. Here, the LOI 710 may convert the modesize down to match that of the SMF 704. The embodiment of FIG. 7 mayfunctionally include a telescope without lenses or critical alignment.The large spot size decreases the tolerance on angle of incidenceincluding variation of the interface angle θ, so it may be taken intoaccount in optimization of the surface coupled system 700 of FIG. 7.

FIG. 8 illustrates an overhead view and cross-sectional views of anotherexample LOI 800, arranged in accordance with at least one embodimentdescribed herein. The LOI 800 may include or correspond to the LOI 310of FIGS. 3 and 4, or to the LOI 710 of FIG. 7, or to other LOIs in othersurface coupled systems described herein.

In the example of FIG. 8, the LOI 800 includes two waveguide cores 802A,802B (collectively “waveguide cores 802”) and surrounding cladding 804that together form the LOI waveguide of the LOI 800. The two waveguidecores 802 may include both a SiN waveguide core 802A and a Si waveguidecore 802B aligned to overlap both laterally (e.g., in the y direction)and longitudinally (e.g., in the z direction). The SiN waveguide core802A may be tapered, e.g., relatively narrow at an input end 806 of theLOI waveguide and widening from left to right along at least a portionof the length of the SiN waveguide core 802A to be relatively wider atan output end 808 of the LOI waveguide, similar to the waveguide core502 of FIG. 5. The Si waveguide core 802B may also be tapered, narrowingfrom left to right, and may be completely absent at the output end 808of the LOI waveguide.

The two cross-sectional views include the cross-sectional view on theleft, taken near the input end 806 where the waveguide cores 802 overlapin the y and z directions, and the cross-sectional view on the right,taken near the output end 808 where the Si waveguide core 802B isabsent. Each of the cross-sectional views includes a representation ofthe optical mode 810, 812 at the corresponding location.

The optical mode out of a transmit grating (or first surface grating) ofa corresponding GCL laser may be exponential in intensity profile if thetransmit grating is not apodized. In these and other embodiments, the Siwaveguide core 802B may be provided beneath the SiN waveguide core 802Ain the LOI 800 to modify the optical mode to better overlap with theoptical mode of the transmit grating. The Si waveguide core 802B may belocated about 100 nm beneath the SiN waveguide core 802A in someembodiments.

As indicated above, some embodiments described herein may have lowerloss, wider bandwidth, and/or less back reflection than theconfiguration of FIG. 1. For example, some embodiments of LOIs asdescribed herein may have loss lower than 1 decibel (dB) and a bandwidthof about 100 nanometers or more. In these and other embodiments, the LOImay be designed to accept about a 30 μm Gaussian optical mode from a GCLlaser. The 30 μm Gaussian optical mode may be equivalent to a Gaussianoptical mode with a w₀ parameter of 15 μm. The LOI may include alow-contrast oxide waveguide with a tapered SiN waveguide core that hasa relatively thin/narrow tip. The LOI may also include a spot sizeconverter (SSC) section that transitions from the low-contrast waveguideto a high-contrast waveguide. The LOI may include or be coupled to anangled facet, such as the input interface 316 of FIG. 3, to direct lightinto the LOI waveguide.

FIG. 9 is a cross-sectional view of another example LOI 900, arranged inaccordance with at least one embodiment described herein. The LOI 900may include or correspond to one or more of the other LOIs describedherein. The LOI 900 may include a waveguide core 902, a cladding 904,and a substrate 906. Alternatively or additionally, the LOI 900 mayinclude an air cladding 908.

The waveguide core 902 may include SiN or other suitable material. Thewaveguide core 902 may have a width w_(core) and a height h_(core) whichmay be constant or variable along a length (e.g., coming in and out ofthe page) of the waveguide core 902. For instance, the waveguide core902 maybe tapered in width, similar to the waveguide cores discussedabove, or in height. Alternatively or additionally, the LOI 900 mayinclude additional waveguide cores above or below the waveguide core 902along at least some portions of the length of the LOI 900. In an exampleembodiment, and at a location of the cross-sectional view of FIG. 9, thewidth w_(core) may be about 0.5 μm and the height h_(core) may be about25 nm.

The cladding 904 may include SiO₂ or other suitable material. Thecladding 904 may have a rib-type cross-sectional profile with a ridgewidth w_(ridge), a ridge height h_(ridge), a rib height him, and a ribwidth writ. In an example embodiment, and at the location of thecross-sectional view of FIG. 9, the ridge width w_(ridge) may be about35 μm, the ridge height h_(ridge) may be about 13 μm, the rib height himmay be about 20 μm, and the rib width writ may be about 30 μm. One ormore of the other LOIs described herein may similarly be implementedwith a cladding that has a rib-type cross-sectional profile.

The substrate 906 may include Si or other suitable material. One or moreof the other LOIs described herein may similarly be implemented with asubstrate.

The air cladding 908 may help to lower guiding mode effective index,leading to a larger mode profile. One or more of the other LOIsdescribed herein may similarly be implemented with an air cladding.

The LOI 900 may be optimized or configured for single-polarizationoperation. For example, the LOI 900 may have an input optical mode(e.g., an optical mode at its input end) that matches or substantiallymatches an output optical mode of a GCL laser for TE polarized light andmay modify the optical mode to match, at an output of the LOI 900, aninput optical mode of a SMF or Si PIC for the TE polarized light.

FIG. 10 illustrates a simulated supported optical mode 1000 of the LOI900 of FIG. 9, arranged in accordance with at least one embodimentdescribed herein. The simulation of FIG. 10 shows an effective indexNeff of the LOI 900 at its input end is Neff=1.4463+i1.49E−6, which maycorrespond to a propagation loss of 0.62 dB/cm. In FIG. 10, thesimulated supported optical mode 1000 has a mode field diameter in thevertical direction (MFD(v)) of about 22 μm, a mode field diameter in thehorizontal direction (MFD(h)) of about 24 μm, and a mode overlap with a30 μm Gaussian optical mode (e.g., the assumed optical mode for the GCLlaser output) of 91%, or a 0.45 dB coupling loss.

FIG. 11A includes a cross-sectional view of another example LOI 1100,arranged in accordance with at least one embodiment described herein.The LOI 1100 may include or correspond to one or more of the other LOIsdescribed herein. The LOI 1100 may include a first waveguide core 1102,a cladding 1104, and a substrate 1106 may be the same as or similar tothe waveguide core 902, the cladding 904, and the substrate 906 of FIG.9. Alternatively or additionally, the LOI 1100 may include an aircladding (not illustrated). The LOI 1100 additionally includes a secondwaveguide core 1108 vertically positioned above the first waveguide core1102. The first and second waveguide cores 1102 and 1108 may beseparated by cladding 1104 or other materials or layers. The first andsecond waveguide cores 1102 and 1108 may be separated by a distance d.The distance d may be about 25 nm in some embodiments. The first andsecond waveguide cores 1102 and 1108 may include SiN or other suitablematerials.

FIG. 11B includes an overhead view of the first and second waveguidecores 1102, 1108, arranged in accordance with at least one embodimentdescribed herein. With combined reference to FIGS. 11A and 11B, the LOI1100 may include a low-contrast waveguide (LCWG) section 1110, a SSCsection 1112, a high-contrast waveguide (HCWG) section 1114, and anevanescent coupling section 1116.

In the LCWG section 1110, the second waveguide core 1108 is absent andthe first waveguide core 1102 has a width w_(core1) (e.g., in the ydirection) that tapers laterally outward from a tip width to anintermediate width. In some embodiments, the tip width may be about 0.5μm and the intermediate width may be about 7-8 μm. In the LCWG section1110, the LOI waveguide of the LOI 1100 may have a low index contrast toaccommodate a relatively larger optical mode 1118 that may match orsubstantially match an optical mode of light output by a GCL laser. Theoptical mode 1118 may be relatively weakly guided by the LCWG section1110.

The first waveguide core 1102 may have a constant width (e.g., equal tothe intermediate width) in one or more of the SSC section 1112, the HCWGsection 1114, and the evanescent coupling section 1116. In otherembodiments, the first waveguide core 1102 may have a variable width inone or more of the SSC section 1112, the HCWG section, and theevanescent coupling section 1116.

In the SSC section 1112, which may also be referred to as a verticaltaper section, the second waveguide core 1108 may have a thicknesst_(core2) (e.g., in the z direction) that tapers vertically upward froma tip thickness to an intermediate thickness. The tip thickness may beabout 0 nm and the intermediate thickness may be about 250 nm. The SSCsection 1112 may convert a relatively weakly guided optical mode fromthe LCWG section 1110 to a more highly confined optical mode. Forexample, the optical mode 1118 may enter the SSC section 1112 and get c,converted partially through the SSC section 1112 to a more confinedoptical mode 1120 and then by the end of the SSC section 1112 to an evenmore highly confined optical mode 1122.

FIG. 11A additionally illustrates an example Si PIC 1124 that mayinclude, among others, a substrate 1126, a SiN waveguide core 1128, andcladding 1130. The SiN waveguide core 1128 may have a tapered endaligned in the y and z directions with the second waveguide core 1108 inthe evanescent coupling section 1116 and spaced apart from the secondwaveguide core 1108 in the x direction. The SiN waveguide core 1128 andthe cladding 1130 may form a SiN waveguide of the Si PIC 1124.

In the HCWG section 1114, the optical mode 1122 may generally bemaintained. However, near or after an end of the HCWG section 1114, theoptical mode 1122 may begin to evanescently couple to the SiN waveguideof the Si PIC 1124, as represented by optical mode 1132. By the end ofthe evanescent coupling section 1116, most of the light from the LOI1100 may be coupled into the Si PIC 1124, as represented by optical mode1134.

The second waveguide core 1108 is illustrated in FIG. 11B as having awidth w_(core2) that is constant throughout the SSC section 1112, theHCWG section 1114, and the evanescent coupling section 1116. In otherembodiments, the width w_(core2) of the second waveguide core 1108 mayvary (e.g., by lateral taper) in one or more of the SSC section 1112,the HCWG section 1114, and the evanescent coupling section 1116.

In some embodiments, following the evanescent coupling section 1116, thethickness t_(core2) of the second waveguide core 1108 may tapervertically downward from the intermediate thickness to the tipthickness.

FIG. 12 illustrates a portion of the LOI 1100 of FIG. 11A, arranged inaccordance with at least one embodiment described herein. FIG. 12additionally illustrates light 1202 that may have the various opticalmodes 1118, 1120 (FIG. 11A), 1122 as it propagates through the LOI 1100.The SSC section 1112 may have a length l_(SSC). The length l_(SSC) ofthe SSC section 1112 may influence conversion efficiency from theoptical mode 1118 to the optical mode 1122 in the LOI 1100. Conversionloss in the SSC section 1112 may be simulated by the Eignemode expansionmethod (Lumerical EME).

FIG. 13 is a simulation 1300 of conversion efficiency as a function oflength l_(SSC) of the SSC section 1112, arranged in accordance with atleast one embodiment described herein. As illustrated in FIG. 13, theconversion efficiency may exceed 90% for length l_(SSC) of the SSCsection 1112 of 1.5 millimeters (mm) or longer.

FIG. 14 illustrates the LOI 1100 and the Si PIC 1124 of FIG. 11A,arranged in accordance with at least one embodiment described herein.The total coupling loss of light as it travels from a corresponding GCLlaser through the LOI 1100 to the Si PIC 1124 may be about 1 dB or lessor in some embodiments. Due to the close match (e.g., overlap) betweenthe optical mode of the GCL laser and the optical mode at the input endof the LOI 1100, the total coupling loss may include about a 0.45 dBloss from the GCL laser to the LOI 1100. If the SSC section 1112 (seeFIGS. 11A and 12) has a length greater than 1.5 mm, the total couplingloss may also include about 0.45 dB from the SSC section 1112. The totalcoupling loss may also include about 0.1 dB loss for the transition fromthe LOI 1100 to the Si PIC 1124. Thus, the total coupling loss may beabout 0.45 dB+0.45 dB+0.1 dB=1 dB.

Surface coupled systems that include a GCL laser, an optical isolator, aLOI, and a Si PIC may direct light from the GCL laser into the LOIwaveguide of the LOI in any of a variety of ways, some of which areillustrated in FIGS. 15-20. FIGS. 15-20 include the LOI 1100 and the SiPIC 1124 of FIG. 11A as an example. Other LOIs and/or Si PICS may beimplemented in their place in other embodiments.

In more detail, FIG. 15 illustrates an example surface coupled system1500 with a first laser-to-LOI coupling configuration, arranged inaccordance with at least one embodiment described herein. The surfacecoupled system 1500 includes the GCL laser 302 with the first surfacegrating 306, the optical isolator 320, the LOI 1100, and the Si PIC1124. The GCL laser 302 may be coupled to the optical isolator 320 inthis and other embodiments.

The embodiment of the LOI 1100 illustrated in FIG. 15 includes an inputinterface 1502. The embodiment of the Si PIC 1124 illustrated in FIG. 15includes both the SiN waveguide core 1128 and a Si waveguide core 1504surrounded by cladding 1130. The first laser-to-LOI couplingconfiguration uses the input interface 1502 to redirect light from theGCL laser 302 into the LOI waveguide of the LOI 1100, similar to thesurface coupled system 300 described above. The input interface 1502 mayhave an interface angle determined as described above with respect tothe surface coupled system 300.

In some embodiments, and as illustrated in FIG. 15, the LOI 1100 mayinclude one or more antireflection coating layers 1506 between thesubstrate 1106 and the cladding 1104 of the LOI 1104 to minimize or atleast reduce back-reflection of the light emitted by the GCL laser 302.Other embodiments of the LOI 1100 or other LOIs illustrated in otherFigures may similarly include one or more antireflection coating layersbetween the substrate and the cladding.

In some embodiments, and as illustrated in FIG. 15, the Si Substrate1124 may include the Si waveguide core 1504 included in a layer above orbelow the SiN waveguide core 1128. The Si waveguide core 1504 withsurrounding cladding 1130 may form a Si waveguide. The SiN waveguide andthe Si waveguide of the Si PIC 1124 may be adiabatically coupledtogether, e.g., as described in the '066 patent.

In FIG. 15, the GCL laser 302 and the optical interposer 320 may bedirectly attached to the LOI 1100, e.g., to a bottom or backside of theLOI 1100. The input interface 1502 may be realized as an angled facet bypolishing or other process. A high reflective (HR) coating 1508 may beapplied to the input interface 1502 in some embodiments, while in otherembodiments (e.g., in the case of total internal reflection (TIR)) theHR coating 1508 may be omitted. To use the input interface 1502 as a TIRmirror without the HR coating 1508, equations (1)-(4) above may be usedto determine the angle of the input interface 1502.

FIG. 16 illustrates another example surface coupled system 1600 with asecond laser-to-LOI coupling configuration, arranged in accordance withat least one embodiment described herein. The surface coupled system1600 includes the GCL laser 302 with the first surface grating 306, theoptical isolator 320, the LOI 1100, and the Si PIC 1124. The surfacecoupled system 1600 additionally includes a micro-prism 1602 toimplement the second laser-to-LOI coupling configuration.

The micro-prism 1602 may be assembled together with the GCL laser 302and the optical isolator 320 to convert the light propagation directionfrom the GCL laser 302 and the optical isolator 320 into the waveguideof the LOI 1100. The micro-prism 1602 may be a right-angle prism withits larger surface (e.g., the surface corresponding to the hypotenuse ofthe right angle) having a prism angle θ_(a) determined by an angle ofincidence θ_(i) of light inside the micro-prism 1602. In theconfiguration of FIG. 16, the prism angle θ_(a) may be determinedaccording to equation 5:

θ_(a)=(90°−θ_(i))/2  (5)

In some embodiments, the micro-prism 1602 may include BK7 glass (n˜1.5)or other suitable material. The GCL laser 302, the optical isolator 320,and the micro-prism 1602 may be coupled together as a unit and activelyaligned to the LOI 1100 and Si PIC 1124 in some embodiments.Alternatively or additionally, the micro-prism 1602 may include a HRcoating 1604 on some or all of its larger surface and/or one or more ARcoating layers 1606, 1608 at interfaces with the optical isolator 320and the LOI 1100.

The micro-prism 1602 may have a length l. The length l of themicro-prism 1602 may be about 200 μm in some embodiments.

FIG. 17 illustrates another example surface coupled system 1700 with athird laser-to-LOI coupling configuration, arranged in accordance withat least one embodiment described herein. The surface coupled system1700 includes the GCL laser 302 with the first surface grating 306, theoptical isolator 320, the LOI 1100, and the Si PIC 1124. The surfacecoupled system 1700 additionally includes a Si mirror 1702 to implementthe third laser-to-LOI coupling configuration.

The Si mirror 1702 may be fabricated by wet etch on a Si bench. Aprecise mirror angle of the Si mirror 1702 may be defined by crystalplanes. The third laser-to-LOI coupling configuration of FIG. 17 mayhave a simple integration flow using all parallel components.

FIG. 18 illustrates another example surface coupled system 1800 with afourth laser-to-LOI coupling configuration, arranged in accordance withat least one embodiment described herein. The surface coupled system1800 includes the GCL laser 302 with the first surface grating 306, theoptical isolator 320, the LOI 1100, and the Si PIC 1124. The surfacecoupled system 1800 additionally includes a wedge prism 1802, with theGCL laser 302, the optical isolator 320, and the wedge prism 1802packaged together as a unit and rotated 90 degrees to implement thefourth laser-to-LOI coupling configuration.

The wedge prism 1802 may have an index of refraction n_(prism) and awedge angle θ_(w) (e.g., of bottom surface 1804 relative to vertical).The wedge angle θ_(w) may be determined by the emission angle θ_(i) oflight 1806 from the GCL laser 302 according to equation 6:

θ_(w)=sin⁻¹[(n _(prism) /n _(air))*sin θ_(i)]  (6)

The fourth laser-to-LOI coupling configuration of FIG. 18 may eliminateuse of a high-reflecting plane (as in FIGS. 15-17) to reduce potentialloss that may arise from non-perfect reflectivity of such a plane.

FIG. 19 illustrates another example surface coupled system 1900 with afifth laser-to-LOI coupling configuration, arranged in accordance withat least one embodiment described herein. The surface coupled system1900 includes the GCL laser 302 with the first surface grating 306, anoptical isolator 1902, the LOI 1100, and the Si PIC 1124. The opticalisolator 1902 may be the same as or similar to other optical isolatorsdescribed herein, and/or may include mirror 1904 integrally formed withor attached to a bottom of the optical isolator 1902 to implement thefifth laser-to-LOI coupling configuration.

The mirror 1904 may include a Si mirror, a metal mirror, or othersuitable mirror. For example, the mirror 1904 may include a wet etchedSi mirror for accurate angle. A wafer level process may be implementedto package the optical isolator 1902, the mirror 1904 and the LOI 1100together, e.g., as a unitary component.

FIG. 20 illustrates another example surface coupled system 2000 with asixth laser-to-LOI coupling configuration, arranged in accordance withat least one embodiment described herein. The surface coupled system2000 includes the GCL laser 302 with the first surface grating 306, theoptical isolator 320, the LOI 1100, and the Si PIC 1124. The surfacecoupled system 2000 additionally includes a Si optical bench 2002 with aplatform 2004 and an angled facet 2006 to implement the sixthlaser-to-LOI coupling configuration.

The Si optical bench 2002 may provide a high-reflective well-definedangled facet 2006 of, e.g., 54.7 degrees in an example embodiment, by Sicrystal plane. The GCL laser 302 and the optical isolator 320 coupledtogether as a unit may be mounted to the platform 2004 of the Si opticalbench 2002. The LOI 1100 and the Si PIC 1124 may also be mounted to theplatform 2004 with the LOI 1100 positioned to receive into its LOIwaveguide light 2008 emitted by the GCL laser 302 through the opticalisolator 320 and reflected from the angled facet 2006. Accordingly, theSi optical bench 2002 may provide a common mounting platform for theother components of the surface coupled system 2000.

Assembly of surface coupled systems according to the sixth laser-to-LOIcoupling configuration of FIG. 20 has the potential to be a wafer-levelprocess, which may reduce costs compared to other processes.

Accordingly, FIGS. 3 and 15-20 disclose various components to redirectlight emitted by the GCL laser 302, after the light has passed through acorresponding optical isolator 320 or 1902, into the LOI waveguide ofthe LOI 1100. The components that redirect the light may be genericallyreferred to as light redirectors, one or more of which may be includedin some surface coupled systems to redirect the light from the output ofthe optical isolator into the LOI waveguide of the LOI. Moreparticularly, each light redirector may redirect the light to propagateinto and through the LOI waveguide. For example, a given lightredirector may redirect the light so that it is generally propagatingparallel to and within the LOI waveguide.

Various surface coupled systems described herein include a GCL laser, anoptical isolator, a LOI, and a light redirector. Such systems mayoptionally further include a Si PIC or SMF. Alternatively oradditionally, some embodiments may omit the optical isolator and mayinclude a GCL laser, a LOI, and a light redirector. For example, one ormore of the embodiments illustrated in one or more of the Figures may bemodified to omit the optical isolator.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A system comprising: a grating coupled lasercomprising a laser cavity and a transmit grating optically coupled tothe laser cavity, the transmit grating configured to diffract lightemitted by the laser cavity out of the grating coupled laser; a laseroptical interposer (LOI) comprising an LOI waveguide with an input endand an output end; and a light redirector optically positioned betweenthe grating coupled laser and the LOI, the light redirector configuredto redirect the light received from the grating coupled laser andtraveling in a first direction to travel in a second direction into theinput end of the LOI waveguide, the second direction parallel to the LOIwaveguide.